Directed lighting fixtures traditionally use a light source and a contoured reflective surface to distribute light over a desired pattern or area. If the light source is an incandescent bulb, the bulb may have a diffuse emission pattern, and be positioned at the focal point of a reflector. The reflector directs the light to the desired field of view. Bulbs also have been developed that include internal reflectors to produce spotlight type distribution patterns.
Increasingly, there are a number of lighting applications which require a narrow field of view. A wide variety of reflector structures have been considered for limiting the field of view, but the efficiency of the light distribution produced by the known structures has generally been limited. A traditional source and parabolic reflector actually focuses the emitted light, producing a concentration of the light in a small area within the field of view at a given distance from the lighting fixture. Also, many reflector designs concentrate a substantial portion of the light in the field of view, but allow some portion of the light to escape the desired field, thus limiting the lighting efficiency within the desired field of view.
Recently, interest also has focused on development of lighting systems utilizing optical fibers. Optical fibers allow transport of light from a source to a desired location and direction of the light from an end of the fiber. The emission pattern from most such fiber systems generally produces a pool of light from one or more fibers. Such fiber lighting systems do not provide a narrow field of view with a uniform distribution within the designated field of view.
A need therefore exists for a lighting system which will provide efficient directed lighting, e.g. with a uniform intensity distribution, over a relatively narrow field of view. A need also exists to provide such a lighting system for use with an optical fiber type light source. Disclosure of the Invention The present invention addresses the above stated needs and provides an advance over the art by utilizing a conical deflector. The deflector, for example, may have the shape of a circular cone, but the cone is truncated to have an opening at its narrow end (rather than a point). The deflector is dimensioned relative to the narrow field of view and the light source to deflect light that would otherwise pass out of the desired field of view so as to illuminate the desired field of view. Virtually all of the emitted light illuminates the desired field of view, resulting in a high efficiency of illumination within that field. Also, the conical deflector provides a substantially uniform light intensity distribution over the desired field of view.
In one preferred embodiment, the opening of the narrow end of the conical deflector is coupled to the light emitting end of one or more optical fibers. The angle of the cone of the deflector corresponds to the desired angle of the field of view. The inner surface of the deflector has a specular reflective characteristic over a substantial area thereof. The degree of specular reflectivity may vary over the length of the conical deflector.
Alternate embodiments utilize a combination of one or more of the conical deflectors with a source and an integrating cavity. The narrow end of each cone is coupled to an opening through the wall of the integrating cavity. The light emerging from the cavity includes substantially all of the light emitted from the source. The one or more conical deflectors direct that light uniformly over the desired field of view. In this embodiment, the source may be a lamp or the like within the cavity, or the source may be the light emitting end of one or more optical fibers.
In an embodiment with a single cone coupled to the cavity, the integrating cavity preferably is spherical, with a diffusely reflective surface. In another embodiment with several conical deflectors, the integrating cavity is cylindrical. Other cavity shapes also may be used. In each case, the inner surface(s) of the cavity have a highly diffuse reflective characteristic.
The invention also encompasses a number of techniques to further improve uniformity within the field of view produced by the conical deflector in the basic embodiments discussed above. One approach is to use two or more different types of reflectivity in different sections along the interior surface of the cone. For example, a section of the cone beginning adjacent the opening in the small end of the cone and extending lengthwise to approximately the middle of the cone may have either a diffuse reflectivity or a quasi-specular reflectivity. The rest of the inner cone surface, extending from the middle to the large end of the cone, would have the highly specular reflective characteristic.
The invention also encompasses techniques to produce a desired shape of the field of view of the source and deflector system. The exemplary cone discussed above, having a circular cross-section, typically has a circular field of illumination. Cones having different cross-sectional shapes, for example oval, elliptical, triangular, rectangular or semi-circular (with a flat side) produce correspondingly shaped fields of view for illumination by the source and deflector system. Also, non-circular components sometimes give better performance than circular components.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will because apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.